ANATOMY OF THE NEMATODES 361 



that not only do the borders of the cells disappear, 1 but a fine fibrous 

 differentiation appears in their cytoplasm. The matrix or ectoderm 

 then has the appearance of an ectodermal syncytium permeated by 

 fibres and strewn with nuclei, so that it is hardly distinguishable from 

 the tissue of (3) the CUTIS, which is always present, though developed 

 to a varying degree. Both layers, matrix and cutis, project internally 

 as ridges and form the lateral lines, while the less marked median 

 lines are produced apparently only by the ectoderm (fig. 260). 



Unicellular cutaneous glands are known in parasitic as well as in 

 free-living species ; they vary in number and arrangement, and are 

 found discharging some at the anterior extremity and others in the 

 vicinity of the genital orifices. In other cases large numbers of them 

 are present along the lateral lines ; they are strongly developed in 

 most of the Trichotrachelidcv, where they discharge either along a 

 part of the ventral surface or along the lateral and median lines ; they 

 .are placed so closely together that the ridges of the cuticle perforated 

 by the orifices have long been known, and have been described, as 

 " rodlet borders," or " fields of rods." 



As the cutis is immediately adjacent to (4) the DERMO-MUSCULAR 

 TUBE the simple layer of the muscular cells is divided into four quad- 

 rants by the longitudinal lines two dorsal and two ventral (fig. 260). 

 The MUSCLES are in the simplest cases large rhomboid cells that lie 

 two by two in each quadrant, so that on transverse section of the 

 entire worm only eight cells are perceptible. The outer border of 

 the cells is converted into contractile fibrils, while the contiguous 

 inner portion has remained protoplasmic, and contains the nucleus. 

 In large species the muscular cells do not only increase in length 

 {up to 3 mm.) and in number in every quadrant, but their contractile 

 portion curves up to form a groove (like that of a dead leaf) thereby 

 ven becoming thicker; simultaneously space is gained for more 

 cells, the protoplasmic parts of these cells (on transverse section) pro- 

 ject out of the grooves like vesicles. In all cases there is only one 

 layer of longitudinal muscular cells, which, by contracting, can shorten 

 the body or, by contracting one side, can bend it. In the latter case 

 the muscles of the opposite side have an antagonistic effect, or when 

 all the muscles are contracted, the elasticity of the cuticle acts in the 

 same way. Special muscles exist at the beginning of the gut and at 

 sections of the genital apparatus. 



The existence of a cavity between the body and the gut wall has 

 hitherto been generally assumed, and has been referred to the cleavage 

 cavity, and consequently designated as a primary body cavity. More 



1 In the Ascaridce isolated epidermal cells grow to a considerable size, and have to do with 

 the sensory apparatus of the lips (Goldschmidt). 



